In response to RFA NIAMDD 81-01, the Washington University School of Medicine proposes to select 20 insulin dependent diabetics and randomize 10 of them into an intensively treated group and 10 into a conventionally treated group as part of Phase I and Phase II of the RFA. The specific aims are (1) to demonstrate that our center's previous experience in achieving long term "optimal" or "markedly improved" metabolic control in 29 nonpregnant insulin dependent diabetics can be repeated in 10 10-28 year old patients treated by means of a protocol to be agreed to in Phase I; (2) to demonstrate that improved metabolic control will result in markedly reduced hemoglobin A1c and minimal moderate or severe hypoglycemia; (3) to demonstrate that improved diabetic control with miniature, programmable infusion pumps for open loop insulin delivery will result in improved ocular, neurologic, renal, biochemical, vascular function while achieving a high degree of patient acceptability; (4) to develop rapid, practical methods for calculating 24 hour insulin requirements in diabetics and (5) to begin to develop criteria for optimal patient selection and compliance for Phase III of the proposed studies for both intensively treated and "conventionally treated" diabetics. The facilities, resources and personnel available for this study include (1) Experience in the development, evaluation and application of closed loop and open loop devices for blood glucose control in diabetics; (2) A unique population of research patients with insulin dependent diabetics who have volunteered for studies as part of the Diabetes Registry Program of the Diabetes Research and Training Center; (3) A unique environment of experienced clinical investigators with expertise in treatment of diabetes and its complications in collaborative studies conducted in a General Clinical Research Center with an established participation of a large number of established investigators in the fields of diabetes, diabetic retinopathy, biochemistry, clinical physiology, and clinical psychology.